SEARCH

SEARCH BY CITATION

Keywords:

  • biosphere-geosphere interaction;
  • Holocene climate change;
  • terrestrial carbon cycle dynamics

[1] An inverse method is used to investigate the global carbon cycle from the early Holocene (8 kyr BP) to the end of the pre-industrial period (0 kyr BP) in an improved version of the “green” McGill Paleoclimate Model (MPM). In this paper, we now take into account the vegetation-precipitation feedback and evaluate the terrestrial carbon cycle for the pre-industrial equilibrium. From our coupled transient simulation under orbital forcing, reconstructed (Taylor Dome) atmospheric CO2 forcing and a prescribed retreating Laurentide Ice Sheet (LIS), we find a decrease of 70 PgC in total carbon storage in the Sahara region (15°N to 30°N and 15°W to 50°E), which is caused by the desertification simulated in the green MPM. The above decrease is partially compensated by an increase of 40 PgC in total carbon storage in the Southern Hemisphere from 8 to 2 kyr BP. From an analysis of the total carbon stored under the ice sheet, we can infer that this carbon has negligible impact on atmospheric CO2 after 8 kyr BP. From our model results, we further conclude that the retreating LIS, together with the vegetation-albedo feedback, cause the global terrestrial carbon to increase from 8 to 6 kyr BP. The application of the inverse method suggests that the first 10 ppmv increase in atmospheric CO2 from 8 to 6 kyr BP comes from the ocean. Finally, in the model simulations, the total terrestrial carbon release from 6 to 0 kyr BP is about 68 to 95 PgC, which would produce about a 5 to 7 ppmv atmospheric CO2 increase, based on the calculation of Joos et al. (2004). Owing to our model limitation (there is no ocean carbon cycle), we cannot conclude whether the overall oceanic CO2 release from 8 to 0 kyr BP is due to outgassing related to SST changes or to calcite compensation as proposed by Broecker et al. (2001).